Critical care physician's need a bedside cerebral blood flow monitor (CBF) coupled to cerebral metabolic rate for oxygen (CMRO2). In the context of time-sensitive intolerance of the brain to ischemia/hypoxia management of critically ill patients with neurovascular pathophysiology has always been hindered by inability to easily, repeatedly, and noninvasively, at the bedside~ determine CBF and CMRO2 to facilitate fast diagnosis of ischemia. Many surrogates for this exist. None are satisfactory. Several additional methods require transport of the patient to an imaging suite and thus are not true monitors with added risk of transport. This has resulted in clinicians making therapeutic decisions directed to non-neurologic endpoints, e.g., blood pressure, PaCO2 and so on, hoping that such interventions will have a desired effect on brain perfusion and metabolism. Diffuse Correlation Spectroscopy(DCS) and diffuse optical spectroscopy(DOS) are promising optical techniques under development at UPenn which can provide continuous quantitative rCBF,rCMRO2 and oxygen extraction fraction (OEF) information, respectively, with new technology available to provide for continuous absolute measures of CBF, CMRO2, and OEF. Our long range goal is to prevent the development of in-hospital brain tissue death through development of improved bedside CBF/CMR monitoring techniques that will enable implementation of individualized therapy to prevent such adverse outcomes with their attendant long term disabilities. Our specific aims are to test the hypotheses in neuroICU patients that: 1. Optical monitoring of cortical rCBF indicates subcortical tissue CBF 2. Optical monitoring techniques can detect anaerobic CBF thresholds 3. Optical monitoring techniques can predict anaerobic brain ischemia Noninvasive optical monitoring detection of anaerobic conditions will be confirmed with invasive microdialysis and PbrO2 and low CBF will be confirmed with invasive thermodilution CBF Using invasive monitors as the gold standard for anaerobic ischemia, sensitivity/specificity and pattern analyses will be performed for noninvasive detection and prediction of anaerobic ischemia with optical monitoring. The proposed research will make feasible the notion of protocolized yet individualized goal-directed titration of physiologic and pharmacologic therapy to prevent new brain tissue death in patients admitted with ischemic stroke, intracerebral hemorrhage, subdural hemorrhage, subarachnoid hemorrhage, and traumatic brain injury. These diseases constitute the leading causes of disability in the United States.